How many people in the United Kingdom are nonbinary?by Nat Titman – December 16, 2014
http://practicalandrogyny.com/2014/12/16/how-many-people-in-the-uk-are-nonbinary/Reliable figures show that at least 0.4% of the UK population defines as nonbinary when given a 3-way choice in terms of female, male or another description. That's about 1 in every 250 people. The proportion will likely be higher when the question is phrased in terms of man/woman or when multiple choices are allowed, as is shown in studies of trans and asexual populations.
Identities and experiences under the nonbinary umbrella are extremely diverse with many identifying with multiple labels. Only around 31% of nonbinary people confidently identify as trans and more than 65% are not protected by the Equality Act 2010 gender identity provisions. Surveys of trans communities found around 25 to 28% identify in some way outside of the binary.